Mode-Specific Dynamics Studies for the Multichannel C₂H₂ + OH Reaction

The C₂H₂ + OH reaction is a key elementary reaction in acetylene oxidation, and the products forming in different reaction channels, such as C₂H and CH₃ radicals, are also important for subsequent reaction processes in the combustion process. In this work, we investigated the dynamics of the C₂H₂ + OH reaction with specific vibrational mode excitations and analyzed the mode specificity based on quasi-classical trajectory calculations on a recently developed full-dimensional potential energy surface. It is found that exciting OH stretching mode can promote the production of H + OCCH₂ and CO + CH₃, while the excitation of C-H symmetric/antisymmetric stretching mode of C₂H₂ can facilitate the H₂O + C₂H channel. Based on the prediction of vibrationally adiabatic and sudden vector projection models, the mode specificity in the C₂H₂ + OH reaction can be attributed to the difference in the degree of coupling between the initial motion mode and the reaction coordinate of each reaction path, which ultimately leads to the changes in rate constants and the product branching ratios. These findings can offer theoretical insights to regulate the branching ratio of the multichannel C₂H₂ + OH reaction.